Light emitting devices, such as Light Emitting Diodes (LEDs) or Laser Diodes (LDs), which use group III-V or group II-VI compound semiconductors, are capable of emitting light of various colors, such as red, green, blue, and ultraviolet light and the like, owing to developments of device materials and thin film growth technologies. Moreover, these light emitting devices are capable of emitting white light with high efficiency through use of a fluorescent substance or color combination, and have advantages of low power consumption, semi-permanent lifespan, fast response time, safety and environmental friendliness as compared to conventional light sources, such as fluorescent lamps, incandescent lamps and the like.
Accordingly, application sectors of light emitting devices are expanded up to transmitting modules of optical communication means, LED backlights to replace Cold Cathode Fluorescence Lamps (CCFLs) which serve as backlights of Liquid Crystal Display (LCD) apparatuses, white LED lighting apparatuses to replace fluorescent lamps or incandescent lamps, head lights of vehicles and traffic lights.
A light emitting device package includes a first electrode and a second electrode arranged over a package body and a light emitting device arranged at a lower surface of the package body and electrically connected to the first electrode and the second electrode.
FIG. 1 is a view illustrating a conventional light emitting device package.
The light emitting device package 100 may include package bodies 110a, 110b, and 110c, which internally define a cavity, and a light emitting device 140 placed on a bottom surface of the cavity. A heat dissipation member 130 may be placed in the package bodies 110a and 110b below the package body 110c. The heat dissipation member 130 and the light emitting device 140 may be fixed via a conductive adhesive layer (not shown).
The cavity is filled with a molding part 150 to surround and protect the light emitting device 140. The molding part 150 may contain a fluorescent substance 160. The fluorescent substance 160 is excited by a first wavelength band of light emitted from the light emitting device 140, thereby emitting a second wavelength band of light.
However, the conventional light emitting device package has the following problems.
In FIG. 1, the heat dissipation member 130 may be formed of a highly thermally conductive material such that heat generated from the light emitting device 140 of the light emitting device package 100 is emitted through the heat dissipation member 130.
In this case, if thermal expansion of the heat dissipation member 130 occurs, this may cause damage to the light emitting device 140. For this reason, a ceramic layer 120, for example, may be placed over the heat dissipation member 130 to prevent damage to the light emitting device 140 due to thermal expansion of the heat dissipation member 130.
However, when the ceramic layer 120 is provided over the heat dissipation member 130, stress may be applied to the ceramic layer 120 above the boundary of the heat dissipation member 130 and the package body 110b due to mismatch between the coefficient of thermal expansion of the heat dissipation member 130 and that of the package body 110b during a co-firing process for fabrication of a ceramic package. This may cause cracking in the ceramic layer 120 within the co-fired package as exemplarily shown in region ‘A’ of FIG. 1. That is, the ceramic layer 120 may be damaged by coefficient of thermal expansion mismatch between different kinds of materials, and deterioration in the hermetic seal durability of the light emitting device package 100 may cause lifespan reduction after extended operation or upon operation under high humidity environments.